A human rights group in Papua New Guinea says more than 1,000 people have marched on the streets of Buka to protest against the murder of an elderly woman accused of sorcery.

The North Bougainville Human Rights Committee (NBHRC), citing police sources, says the woman was allegedly beheaded on Friday in Bana District, South Bougainville.

A police spokesman says Helen Rumbali and three others were kidnapped by relatives of a former school teacher who died recently.

NBHRC's chairperson Helen Hakena says Ms Rumbali's elderly sister Nikono is fighting for her life after being tortured.

Ms Hakena has told Radio Australia the majority of people attending the mass rally on Monday have condemned the "inhumane killing."

"The general feeling today from everyone who was there was sadness," she said.

"There were over 1,000 people, particurlay women who outnumbered the men.

"Most of the women who were there really spoke out and condemned the barbaric killing of another woman, particularly during this peace time in Bougainville.

"Even though we were fighting ten years ago, men or ex-combatants still respected life...even the ex-combatants who came out and spoke out today - they condemned the barbaric killing and torture of Helen Rumbali."

The killing comes just days after another report that six women accused of sorcery were tortured with hot irons in a so-called Easter "sacrifice" in the Southern Highlands.

Last month, a woman accused of sorcery was stripped naked and burned to death by a mob, with Amnesty International stepping up calls for an end to sorcery-related violence in Papua New Guinea.

Amnesty has urged the PNG Government to stamp out the practice in the Pacific nation where there is a widespread belief in sorcery and where many people do not accept natural causes as an explanation for misfortune and death.

There have been several other cases of witchcraft and cannibalism in PNG in recent years.